(Corrects this story from July 30 to show Theo van Gogh was Vincent van Gogh’s great grand nephew not great grandson.)

AMSTERDAM (Reuters) - Dutch police conducted security searches around Amsterdam’s Schiphol airport on Saturday in response to “indications” of a threat, an official said, causing traffic jams during the busy summer holiday season.

The National Coordinator for Counter-terrorism and Security Policy (NCTV) provided no details of the possible threat, but it said extra security measures were implemented, including vehicle searches.

“There was a (threat) indication related to the airport,” said spokesman Edmond Messchaert. “The increased measures are intended to ensure the safety of people working at the airport and travellers.”

The national threat level in the Netherlands was unchanged at “substantial,” or one notch from the highest.

After attacks by Islamist radicals in France, Belgium and Germany, the Netherlands is considered a prominent target, because it supports U.S.-led military operations against Islamic State in the Middle East.

The last major attack in the Netherlands was the killing by a Muslim radical of Theo van Gogh, the outspoken, film maker and great grand nephew of the famous painter, in 2004.